Putting an image texture onto a selfmade object
Thre's no need for so much seams.
A very simple UV map is enough.




(Repair the mesh - more steps below) :)
Add just a few seams where needed
Use the UV editor to position the UV map
Set image texture to Clip - so it's not repeated across the model.


Using just one material is very limiting, but sometimes needed.
Use more materials if you want different color on your mesh.

Example of a proper UV unwrap





How to repair the mesh:


Apply object scale and rotation through Object > Apply > All transforms
Remove stray and connect unconnected vertices/faces/edges
Make the mesh manifold (watertight)
Correct face orientation through Mesh > Normals > Recalculate outside
Delete the old UV map entirely


Here is a repaired .blend for inspiration.
Yours might look a bit different, but that doesn't really matter :).